Ar-41 source term investigation in HTR-PM: Theory, calculations, and experiments

Ar-41 is a significant activation product in high-temperature gas-cooled reactors (HTGRs). Based on the design and operational parameters of a high-temperature gas-cooled reactor pebble-bed module (HTR-PM), we analyzed the Ar-41 source and constructed an Ar-41 source-term calculation model for HTGRs. For the first time, we presented the measured data of Ar-41 activity in the primary coolant of HTR-PM: during startup, the experimental value could reach up to 10⁹ Bq·m⁻³, consistent with the theoretical prediction of 1.99×10⁹ Bq·m⁻³; during normal operation, that fluctuated between 10⁶ and 10⁸ Bq·m⁻³, in agreement with the theoretical value of 3.27×10⁷ Bq·m⁻³. The effective dose rates for workers in the reactor, steam generator, helium purification system, and fuel loading and unloading compartments are 4.87×10^-2, 3.17×10^-4, 2.17×10^-5, and 9.23×10^-6 Sv·d^-1, respectively. The largest effective dose rate for adult members of the public within an 80 km radius from the plant is 6.61×10^-8 Sv·d^-1. In addition, the key factors that can affect the Ar-41 activity in the primary coolant and the effect of Ar-41 on the activity concentration conversion factor of the gross γ monitoring instrument were discussed. This work provides an important reference for studying the radiation safety in advanced nuclear energy systems and fusion reactors.